1. Arctic sea ice melt in summer 2007: Sunlight, water, and ice NSIDC Sept 2007

2. A long list of suspects Examine the mass balance of the ice Warmer air temperature Longer melt season Winds Export of perennial ice Advection of ocean heat Clouds Enhanced solar heating Ice albedo feedback

3. Sea ice mass balance Simple, but powerful observation Simple concept ice growth surface melt bottom melt Equipment ablation stakes and thickness gauges autonomous buoys Powerful tool – attributes change Above Below

4. Monitoring the mass balance Observations in Beaufort and North Pole http://www.crrel.usace.army.mil/sid/IMB

5. Summer ice melt Interannual variability, latitude influence on surface melt

6. Summer ice melt 2007 at North Pole – typical melt

7. Summer ice melt 2007 Beaufort – typical surface melt

8. Summer ice melt 2007 Beaufort – huge increase in bottom melt

9. Beaufort Sea buoy End of August – peak bottom melt 20-40 40-60 60-80 80-100 150 km August 27

10. Beaufort Sea buoy End of August – peak bottom melt 20-40 40-60 60-80 80-100 150 km August 27 Warmer air temperature Longer melt season Winds Export of perennial ice Advection of ocean heat Clouds Enhanced solar heating Ice albedo feedback

11. Estimate of solar heating Incident solar, ice concentration, and albedo -> heat input F ocn = F r (1 –  ) (1 – C) Input: 25 x 25 km equal area grid Incident (F r ) from ERA-40, ECMWF Ice concentration (C) - SSMI Water albedo (  ) = 0.07 Output: Solar input to the ocean (F ocn ) Neglect ice for now

12. Mean annual input: 1979 – 2005 Ice edge evident, concentric rings from solar input MJ m -2 3 MJ m -2 = 1 cm m -2 of ice melt

13. Percent anomaly in 2007 Heat input near buoy 400 to 500 % greater through 22 Sept 800 700 600 500 400 300 200 100 0 -100 -200 -300 Percent

14. 2007 vs “climatology” Similar incident shortwave, but much less ice

15. Solar heat input Total heat needed for bottom melting

16. Solar heat input Twice as much solar heat even without ice transmitted

17. Conclusions Was there a trigger? North Pole business as usual Beaufort Sea typical surface melt huge bottom melt Solar incident comparable Ice concentration much less Solar input twice melt Ice albedo feedback

18. …

19. Solar heat input Peak ocean heat flux with ice convergence/divergence

20. Total solar heat input to ocean Heat input near buoy from 600 to 800 MJ m -2 through 22 Sept 2007 Units = MJ m -2 3 MJ m -2 ~ 1 cm thinning

21. Percent anomaly in 2007 General increase

22. Incident shortwave anomaly Not much of a difference Incident shortwave from reanalysis Pan – Arctic Ocean 25 x 25 km equal area grid Average 1979 – 2005 (2007 – average) % anomaly %

23. 27 year trend of annual ocean solar heat input Units are percent per year Increasing solar heat input in 89% of area